1. Field of the Invention
The present invention relates to a storage device that causes a head to float over a rotating storage medium and writes data, and to a storage device controller. In particular, the present invention relates to a storage device that controls the flying height of a head in a constant amount of time from the start of rotation of a storage medium such that the head reaches an appropriate flying height, and to a storage device controller.
2. Description of the Related Art
Conventionally, in storage devices represented by HDD (Hard Disk Drive), it has been necessary to lower the flying height of a head with respect to the recording surface of a storage medium such as a magnetic disk in order to realize high recording density. In recent years, a flying height of the extremely small order of 10 nm or less has been realized.
However, when the flying height of the head drops, it becomes easier for the head to collide with minute projections on the magnetic disk surface. Further, because variations in clearance per head are present within a mechanical tolerance range, there is the problem that, in consideration of medium contact, the flying height cannot be set low beyond the tolerance range.
Thus, a method of controlling the clearance between the head and the recording surface of the magnetic disk by installing a heater in the head and utilizing the protrusion phenomenon that results from the thermal expansion of the head floating surface accompanying the supply of power to the heater has been proposed (Japanese Laid-open Patent Publication No. 2003-168274).
Further, a method has been proposed where, as in Japanese Laid-open Patent Publication No. 2005-071546, the change in the protruding amount (TPR amount) resulting from a phenomenon (thermal protrusion: TPR) where the head floating surface protrudes in the direction of the magnetic disk is measured by testing or the like and retained in advance on the magnetic disk, and this data is used to manage the flying height per head.
However, adjustment of the head flying height by testing as disclosed in Japanese Laid-open Patent Publication No. 2005-071546 is performed on the basis of a state where the environmental temperature of the storage device has reached a stable or steady state. For that reason, in an environmental temperature during a transitional period until the environmental temperature reaches a steady state, such as immediately after startup of the storage device, the flying height of the head is not invariably an optimum flying height.
Usually, immediately after the storage medium disposed in the storage device begins rotating, such as when the power of the storage device is turned ON and the storage device begins operating, or when the power of the storage device is already ON and the storage medium resumes rotation after being stopped such as during a power saving mode, the environmental temperature of the storage device is lower than in the steady state. For that reason, the flying height of the head ends up being higher than the flying height in the steady state. For example, it is known that, as shown in FIG. 7, immediately after startup of a storage device, the flying height of the head is about 0.4 to 0.6 nm higher than the flying height in a steady state. Further, it is known that it takes about 10 minutes for the head to reach a state where it can operate appropriately at the value that has been preset at the design stage or during testing, that is, for the head to reach the steady state.
Further, with respect to changes in a short amount of time in the local environmental temperature in the vicinity of the head and the magnetic disk, it is also difficult to control the flying height using a temperature sensor because it is difficult to dispose a temperature sensor in the vicinity of the head or the like.
For that reason, within the amount of time until the storage device reaches the steady state immediately after startup, the flying height of the head is higher than in the steady state when the storage device is operated in a condition that has been appropriately set with respect to the steady state of the storage device. Due to this, the reading and writing characteristics of the storage device, and particularly the writing characteristic that is easily affected by the flying height, end up dropping. As a result, the storage device fails at writing and also fails at reading thereafter.
Thus, it is an object of the present invention to make the head fly at an appropriate flying height until the environmental temperature of the storage device reaches a steady state immediately after startup. It is also an object of the present invention to provide a storage device with greater reliability whose characteristics during reading and writing during this time are improved.